1. Field of the Invention
The present invention relates to a disk drive with a head used to read and write data from and to a disk. More particularly, it relates to a method for retracting the head to a ramp provided near the disk, upon the interruption of power to the disk drive, and relates to the disk drive employing the method.
2. Description of the Related Art
As typical disk drives using a disk as a recording medium, hard disk drives (HDDs) are well known. HDDs comprise a head (magnetic head) used to read and write data from and to a disk, and a spindle motor used to rotate the disk. The head is supported by an actuator so that it can move radially over the disk. The actuator has a voice coil motor used to drive the actuator.
When the HDD is in a state in which the head is ready for a read or write operation, the head is positioned above the disk. More specifically, the head is floating over the disk in accordance with the rotation of the disk. When the head performs a read or write operation, it is moved to a target position on the disk by the actuator. In contrast, when the HDD is in the inoperative state, the head is retracted on a particular place (retraction area) called a ramp. The ramp is located outside the recording area of the disk.
If unintentional interruption of power occurs when the head is floating over the disk, it is strongly possible that the head will stick to the disk. To avoid this, various head retraction methods for automatically retracting the head to the ramp upon the interruption of power to the HDD have been proposed so far. Jpn. Pat. Appln. KOKAI Publication No. 2002-298530 discloses one (hereinafter referred to as “the prior art”) of such retraction methods. The prior art is characterized in that the back electromotive force (back EMF) of the spindle motor and the charge accumulated in a capacitor are utilized for head retraction. The head retraction performed upon the interruption of power, disclosed in the prior art, is mainly realized by first and second retract operations. In the first retract operation, the voice coil motor is powered by the back EMF of the spindle motor. As a result, the head is moved to the position (retraction switching position) near the ramp. In the second retract operation, the voice coil motor is powered by the charge accumulated in the capacitor, whereby the head is moved to the ramp.
In accordance with the recent development of microfabrication of HDDs (microfabrication of disks), 1.8-inch HDDs, 1-inch HDDs and even 0.85-inch HDDs have come to be available. In accordance with the reduction of the HDD size, the torque (inertia) of the spindle motor inevitably reduces. Accordingly, when the power to the HDD is interrupted, the smaller the HDD (the smaller the diameter of the disk of the HDD), the more quickly the rotational speed of the spindle motor reduces. Therefore, in the prior art, it is possible that before the head reaches the ramp, the rotational speed of the spindle motor will become less than a value that is required to keep the floating level of the head constant. The lower the ambient temperature, the more conspicuous this tendency. In the prior art, when the supply of power is interrupted at, in particular, low temperature, it is difficult to prevent the head from contacting the disk.